Fabrication of Anisotropic Cu Ferrite-Polymer Core-Shell Nanoparticles for Photodynamic Ablation of Cervical Cancer Cells

Abstract

In this work we developed methylene blue-immobilized copper-iron nanoparticles (MB-CuFe NPs) through a facile one-step hydrothermal reaction to achieve a better phototherapeutic effect. The Fe/Cu ratio of the CuFe NPs was controllable by merely changing the loading amount of iron precursor concentration. The CuFe NPs could serve as a Fenton catalyst to convert hydrogen peroxide (H₂O₂) into reactive oxygen species (ROS), while the superparamagnetic properties also suggest magnetic resonance imaging (MRI) potential. Furthermore, the Food and Drug Administration (FDA)-approved MB photosensitizer could strongly adsorb onto the surface of CuFe NPs to facilitate the drug delivery into cells and improve the photodynamic therapy at 660 nm via significant generation of singlet oxygen species, leading to enhanced cancer cell-damaging efficacy. An MTT (thiazolyl blue tetrazolium bromide) assay proved the low cytotoxicity of the CuFe NPs to cervical cancer cells (HeLa cells), namely above 80% at 25 ppm of the sample dose. A slight dissolution of Cu and Fe ions from the CuFe NPs in an acidic environment was obtained, providing direct evidence for CuFe NPs being degradable without the risk of long-term retention in the body. Moreover, the tremendous photo-to-thermal conversion of CuFe NPs was examined, which might be combined with photodynamic therapy (PDT) for promising development in the depletion of cancer cells after a single pulse of deep-red light irradiation at high laser power.

Keywords: Fenton reaction; bimetallic nanoparticles; cancer treatment; photodynamic therapy; reactive oxygen species; superparamagnetic nanoparticles.

Figure 1

(a) UV–visible spectrum and (b) X-ray diffraction (XRD) pattern of CuFe nanoparticles (NPs). (c) Hysteresis loops of CuFe NPs with different Fe/Cu ratios. (d) Quantification of H₂O₂ catalytic ability by 2′,7′-dichlorofluorescein diacetate (DCFH-DA, n = 4. *** p < 0.001, compared to Fe/Cu ratio of 2).

Figure 2

Photos of CuFe NPs under magnetic field after 0, 5, 15 min and the side view of CuFe NPs under magnetic field after 15 min.

Figure 3

(a) The photothermal effect of CuFe NPs at 100 ppm metal with Fe/Cu ratio of 0 and 2 in DI water or in (b) culture medium. (c) The UV–visible spectrum of methylene blue (MB)-CuFe NPs of Fe/Cu ratio of 0 and (d) 2 at different reaction times. Note that MB has an absorbance peak at a wavelength of 660 nm.

Figure 4

Transmission electron microscopy (TEM) images of CuFe NPs. (a,b) Fe/Cu ratio of 0 shows a single-core structure. (c,d) Fe/Cu ratio of 2 shows a multi-core structure.

Figure 5

(a) Hydrodynamic diameter and (b) zeta potential of MB-CuFe NPs before and after MB conjugation. (c) The UV–visible spectrum of the N,N-dimethyl-4-nitrosoaniline (RNO)/imidazole-treated MB-CuFe NPs solution before and after laser irradiation for 10 min. The peak at 440 nm indicates the existence of RNO reagent, which can be degraded by reactive oxygen species (ROS). (d) Cell activity of cervical cancer HeLa cells after 24 h co-incubation with MB-CuFe NPs. Over 80% of the cells are viable at a metal concentration of 25 ppm in the group with an Fe/Cu ratio of 2.

Figure 6

DCFH-DA fluorescence performance at different metal ratios and different metal concentrations. The stronger fluorescence signal indicates more ROS are generated. (Scale bar: 100 μm).

Figure 7

Cell activity of HeLa cells with and without laser irradiation. (** p < 0.01; MB-CuFe NPs co-incubation time: 4 h).